We are facing an surprising problem in oracle 10g database. Previously we are able to connect our Oracle 10g database using os authentication with "sqlplus / as sysdba" command.

Last wednesday in our linux server maximum number of processes have overflowed and we need to increase the soft limit of our linux server. After that without restarting database every applications [OID 10g] are working fine.

But, we are not able to connect with system using OS authentication. It is showing following.

As you were previsously able to connect to the database using OS authentication. And it can be seen that OS authentication is still enable on you database server. The basic problem would be that you have not exported the sid,home and path variable properly. check the same.

I am agree with saurabh, your OS authentication works fine, when you run sqlplus / as sysdba command, you connected to an instance it says: "connected to an idle instance". so the problem is your environment variables. you should give wrong value either ORACLE_SID or ORACLE_HOME (there might be 2 different home on your server).

check your TNSNAMES.ORA file and look for OID alias and in its description, what is the name of database ? (or service_name)

Is there something to do with OS process? Last wednesday our server are exhausted with many processes and we have increased softlink number in our server. After that we hv not restarted the DB or linux server.

In the previous posts, you appended the oracle home to the PATH. In the last one, you prepended the oracle home to the path. What happens when you echo $PATH? Do you have more than one oracle home? Perhaps the instance that is running got started with the wrong one.

What does ipcs tell you? Are there any shared memory areas you don't recognize? Anything odd in /tmp or ls -rl $ORACLE_HOME/dbs? ls -l $ORACLE_HOME/bin/sqlplus $ORACLE_HOME/bin/oracle

What does lsnrctl services tell you? Perhaps you have more hosts than you realize. I'm kind of wondering where that extra LONDAN goes. When you do get logged in, show parameters global, db_name and instance.

Maybe there really is a need to reboot linux.

How are you getting to be oaprod? Are there other environment variables being set like TNS_ADMIN or TWO_TASK?